Spiral copper tube and aluminum fin thermosyphon heat exchanger

ABSTRACT

The present invention is directed to a thermosyphon heat exchanger. The thermosyphon system eliminates the need for costly and inefficient moving parts in the cooling system. The system also minimizes failures rendering the system inoperable by eliminating mechanical components subject to breakdowns that would render the system inoperable. The design of the heat exchanger coils provides for increased efficiency, reduced cost, and simplified construction and maintenance. The system further reduces the energy consumption required for cooling operation while still providing excellent cooling performance.

CROSS REFERENCE TO RELATED APPLICATION AND PRIORITY CLAIM

[0001] This application claims the benefit of Provisional U.S. Patent Application Serial No. 60/207,057, entitled “Spiral Copper Tube and Aluminum Fin Thermosyphon Heat Exchanger”, naming the same inventor as identified herein and filed May 25, 2000.

BACKGROUND OF THE INVENTION

[0002] With the expansion of telecommunication and computer technology, increasing amounts of electronic equipment are required at various commercial and business facilities. To facilitate interconnection and access to such equipment, it is typically installed in a common enclosure. Further, technological advancements are permitting more and more electronic equipment to be fit into increasingly smaller spaces. These forces are combining to produce relatively dense electronic installations that generate increasing amounts of heat. For such equipment to operate properly, it is necessary to provide a relatively stable and comfortable temperature and humidity. This has typically been accomplished through the use of air conditioning for the enclosures housing the equipment.

[0003] Air conditioners used to perform such cooling typically rely on compression and expansion of a working fluid to absorb heat from the area to be cooled and reject this heat into another environment. In addition to being a relatively costly component, the compressors required are typically electrically powered, which results in significant energy consumption. Additionally, the compressors are typically somewhat noisy, which is disadvantageous because the systems used to cool electronic enclosures are frequently located in areas that are occupied on a continual basis. Noise is therefore disrupting to the occupants. Another disadvantage of compressor-based systems is that the compressors and primemovers therefor, electrical or otherwise, are mechanical components that are subject to mechanical failure, which results in downtime of the equipment.

SUMMARY OF THE INVENTION

[0004] The present invention is directed to solving the problems associated with the compressor-based air-conditioning systems of the prior art. The cooling system of the present invention is based on a thermosyphon, which accomplishes heat transfer using the latent heat of vaporization of a working fluid. Thermosyphons do not require compressors, or any other moving part, in the cooling circuit, and are therefore more reliable, consume less energy, and are better suited to use in inhabited areas than their compressor-based counterparts.

[0005] It is therefore an object of the present invention to provide a thermosyphon-based cooling system that dispenses with the need for compressors and other moving parts in the cooling circuit. Another object of the present invention is to provide a low cost air-to-air heat exchanger. Yet another object of the present invention is to provide a heat exchanger with increased efficiency over prior art designs. Still another object of the invention is to provide a heat exchanger coil design that is simpler and less costly to manufacture than prior art designs.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006]FIG. 1 is a drawing of a two-circuit, two-coil thermosyphon in accordance with the present invention adapted for use as an electronic enclosure cooler.

[0007]FIG. 2 is a drawing of a single heat exchanger coil used as a condenser coil in the two-circuit, two-coil thermosyphon of the present invention.

[0008]FIG. 3 is a drawing of a multi-circuit, single-coil thermosyphon in accordance with the present invention adapted for use as an electronic enclosure cooler.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0009] The present invention is directed generally to a thermosyphon heat exchanger, and specifically to a thermosyphon heat exchanger used to cool a cabinet or enclosure housing electrical or electronic equipment. Thermosyphon heat exchangers use the latent heat of vaporization of the working fluid to transfer heat from the evaporator to the condenser. The working fluid flows through the refrigeration circuit by vapor pressure and gravity flow; the refrigeration circuit contains no moving parts.

[0010] A thermosyphon heat exchanger in accordance with the present invention is illustrated in FIG. 1. The heat exchanger comprises an evaporator coil 1, a condenser coil 2, piping 3, four fans 4 a-4 d, a sheet metal enclosure 5, and a working fluid (not shown). The evaporator and condenser coils use a spiral copper tube construction, described in detail below. Spiral tube construction enhances performance of the heat exchanger by increasing the effective inside surface area of the tube.

[0011] The heat exchanger condenser coil 2 is mounted above the evaporator coil 1. Piping 3 interconnects the two coils. The system is charged with a refrigerant such as R-134a, R-410a, a methanol/water mixture, or an ethanol water mixture. There are no moving parts within the refrigeration circuit. Refrigerant is moved through the system due to vapor forces in the evaporator and liquid gravity feed from the condenser. On the evaporator side, two fans move inside cabinet air through the coil causing the working fluid to absorb heat from the interior of the enclosure. On the condenser side, two fans move cabinet exterior air through the condenser coil to extract the heat from the working fluid and reject it outside the enclosure.

[0012] Specifically, the thermosyphon heat exchanger operates as follows. At the beginning of the refrigeration cycle, working fluid, in liquid phase, is located in evaporator coil 1. Fans 4 c and 4 d force heated air from inside the enclosure through evaporator coil 1. As a result, the liquid phase working fluid absorbs heat from the interior of the enclosure to be cooled. As heat is absorbed by the working fluid, it transitions to the vapor phase, and vapor pressure causes the fluid to move upward through the evaporator tube circuits, through interconnecting piping 3 a, and into the top of condenser coil 2.

[0013] Fans 4 a and 4 b force outside air through condenser coil 2, causing the outside air to absorb heat from the working fluid as it passes through the condenser. As the working fluid loses heat to the outside air, it transitions from vapor phase back to liquid phase and flows downward by gravity through condenser 2. Upon arriving at the bottom of condenser 2, the fluid continues to flow by gravity through interconnecting piping 3 b back to the bottom of evaporator 1 to repeat the refrigeration cycle.

[0014] A detailed diagram of condenser coil 2 is shown in FIG. 2. The evaporator coil is of similar construction, the principal difference being the connection of interconnecting piping 3. The heat exchanger coils include a plurality of aluminum fins 6. The fins include holes (not shown) through which copper tubes 7 are inserted. Each copper tube 7 is of hairpin shape, having a hairpin end 8 and a return end 9. The aluminum fins are stacked in parallel fashion, with the holes aligned, and hairpin copper tubes 7 are inserted therethrough, with all of the hairpin ends 8 at one end of the heat exchanger and all of the return ends 9 at the other.

[0015] To provide a continuous working fluid path through the heat exchanger, U-shaped return bends 10 are affixed to the return ends 9 of tubes 7. The sequence in which the return ends are connected determines the tube circuiting through the heat exchanger. The heat exchanger of the present embodiment is constructed using a spiral arrangement, meaning that the second return end of each tube is connected to the first return end of the next tube. This connection arrangement results in a spiral flow path wherein the working fluid flows into a first tube at a first end, through the first tube hairpin bend, back to the first tube second end, through a return bend and into a second tube at a first end, etc.

[0016] One benefit of the spiral tube construction is free draining of the working fluid, because there are no traps in the working fluid flow path. Gravity flow will cause the fluid to flow through each successive tube until it reaches the bottom of the tube circuit. Another benefit of the spiral tube arrangement is improved performance of the heat exchanger. Because the spiral path requires the working fluid to make numerous passes through the heat exchanger, more heat is transferred between the airflow through the fins and the working fluid, resulting in more efficient operation.

[0017] Another novel feature of the heat exchanger of the present invention is illustrated more clearly in FIG. 2b, which shows the return bend end of the heat exchanger coil. The invention is described below in the context of the condenser coil, but the novel features are equally applicable to the evaporator coil. The condenser includes two parallel working fluid circuit paths. A first path begins at inlet 11 a, and a second begins at inlet 11 b.

[0018] Airflow through the heat exchanger is from right to left as shown in FIG. 2b. As air flows through the heat exchanger and passes over the first tube circuit it absorbs heat from the working fluid flowing in that first circuit. The heated air then passes over the second tube circuit path, however, because the air was already heated by the first circuit path its capacity to absorb heat is reduced. Thus the airstream cannot absorb as much heat from the second path as from the first, making the second path less efficient at rejecting heat from the working fluid to the outside air.

[0019] To remedy this problem, the heat exchanger of the present invention includes crossover bends 12 a and 12 b. At crossover bend 12 a, the first path moves from the left side of the heat exchanger to the right. At crossover bend 12 b, the second path switches from the right side of the heat exchanger to the left. Switching the circuit paths relative to the airflow allows each of the parallel circuits to be exposed directly to the outside airflow for part of the circuit. This equalizes the heat transfer of the parallel circuit paths and improves the overall efficiency of the heat exchanger.

[0020] An alternative embodiment of the thermosyphon heat exchanger in accordance with the present invention is the multi-circuit, single-coil thermosyphon illustrated in FIG. 3. This thermosyphon is similar to the two-circuit, two-coil thermosyphon described above, except that single coil 13 serves as both the evaporator and condenser. The single heat exchanger coil 13 includes numerous tube circuits 14. Each circuit uses only a single hairpin copper tube 15.

[0021] The single coil heat exchanger 13 is constructed such that the hairpin ends 16 of tubes 15 are mounted above the open or return ends 17. The open or return ends 17 of the heat exchanger tubes are all sealed into a common header 19. Common header 19 provides a way for the heat exchanger circuit to be easily charged with working fluid.

[0022] Because the common header is located at the lowest point of the heat exchanger, it is ensured that the working fluid is the same for each tube circuit. Prior art single-coil heat exchangers were constructed with each individual tube circuit sealed off from the others. The prior art design required each tube to be individually evacuated and charged, which is both time-consuming and costly. This time-consuming and costly procedure is avoided by the tube circuit design of the present invention.

[0023] Operation of the single-coil thermosyphon heat exchanger is substantially the same as the two-coil version described above. Working fluid is present in liquid phase at the bottom portion (evaporator portion) of heat exchanger coil 13. Fans 18 c and 18 d force warm air from within the enclosure through the lower portion (evaporator portion) of the heat exchanger coil, causing the working fluid to absorb heat from the air. The absorbed heat causes the working fluid to transition from the liquid phase to the vapor phase, and the vapor then rises through the center of the heat exchanger tubes 15.

[0024] As the vaporized working fluid rises, it passes into the upper portion (condenser portion) of heat exchanger coil 13. Fans 18 a and 18 b force outside air through the upper condenser portion of heat exchanger coil 13, causing the outside air to absorb heat from the working fluid. As heat is absorbed, the working fluid transitions from the vapor phase back to the liquid phase and condenses on the inner walls of the heat exchanger tubes 15. The condensed working fluid then flows downward by gravity back to the lower condenser portion of heat exchanger coil 13 and the cycle repeats.

[0025] Additional modifications and adaptations of the present invention will be obvious to one of ordinary skill in the art, and it is understood that the invention is not to be limited to the particular illustrative embodiments set forth herein. It is intended that the invention embrace all such modified forms as come within the scope of the following claims. 

What is claimed is:
 1. A thermosyphon heat exchanger comprising: a) an evaporator coil comprising a plurality of cooling fins and a plurality of hairpin tubes circuited through said fins, said tubes forming at least one working fluid flow path having an inlet and outlet; b) a condenser coil disposed above said evaporator coil, said condenser coil comprising a plurality of cooling fins and a plurality of hairpin tubes circuited through said fins, said tubes forming at least one working fluid flow path having an inlet and outlet; c) piping connecting said outlet of said at least one evaporator coil working fluid flow path to said inlet of said at least one condenser coil working fluid flow path; d) piping connecting said outlet of said at least one condenser coil working fluid flow path to said inlet of said at least one evaporator coil working fluid flow path; and e) a working fluid, said working fluid being present within said working fluid flow paths.
 2. The heat exchanger of claim 1, wherein said heat exchanger further comprises a plurality of fans, wherein at least one fan forces air through said evaporator coil fins and at least one fan forces air through said condenser coil fins.
 3. The heat exchanger of claim 2, wherein said evaporator coil hairpin tubes are interconnected to form a spiral working fluid flow path.
 4. The heat exchanger of claim 2, wherein said evaporator coil hairpin tubes are interconnected to form a plurality of spiral working fluid flow paths.
 5. The heat exchanger of claim 4, wherein said spiral working fluid flow paths include crossover bends disposed so that equal portions of each spiral working fluid flow path are first exposed to airflow through said cooling fins.
 6. The heat exchanger of claim 2, wherein said condenser coil hairpin tubes are interconnected to form a spiral working fluid flow path.
 7. The heat exchanger of claim 2, wherein said condenser coil hairpin tubes are interconnected to form a plurality of spiral working fluid flow paths
 8. The heat exchanger of claim 7, wherein said spiral working fluid flow paths include crossover bends disposed so that equal portions of each spiral working fluid flow path are first exposed to airflow through said cooling fins.
 9. The heat exchanger of claim 2, wherein: a) said evaporator coil hairpin tubes are interconnected to form a plurality of evaporator coil spiral working fluid flow paths; b) said evaporator coil spiral working fluid flow paths include crossover bends disposed such that equal portions of each spiral working fluid flow path are first exposed to airflow through said evaporator coil cooling fins; c) said condenser coil hairpin tubes are interconnected to form a plurality of condenser coil spiral working fluid flow paths; and d) said condenser coil spiral working fluid flow paths include crossover bends disposed such that equal portions of each spiral working fluid flow path are first exposed to airflow through said condenser cooling fins.
 10. The heat exchanger of claim 9, wherein said working fluid is selected from the group consisting of: R-134a, R-410a, methanol, ethanol, a mixture of methanol and water, and a mixture of methanol and water.
 11. A thermosyphon heat exchanger comprising: a) a coil comprising a plurality of cooling fins and a plurality of hairpin tubes circuited through said fins forming a plurality of tube circuits; b) a header connecting the open ends of said hairpin tubes; and c) a working fluid contained within said tube circuits.
 12. The heat exchanger of claim 11, wherein said heat exchanger further comprises at least one fan forcing air through said coil fins.
 13. The heat exchanger of claim 11, wherein said working fluid is selected from the group consisting of: R-134a, R-410a, methanol, ethanol, a mixture of methanol and water, and a mixture of methanol and water.
 14. The heat exchanger of claim 12, wherein said working fluid is selected from the group consisting of: R-134a, R-410a, methanol, ethanol, a mixture of methanol and water, and a mixture of methanol and water.
 15. A thermosyphon heat exchanger comprising: a) an evaporator coil comprising a plurality of cooling fins and a plurality of hairpin tubes circuited through said fins, said tubes interconnected to form at least one spiral working fluid flow path having an inlet and an outlet; b) a condenser coil disposed above said evaporator coil, said condenser coil comprising a plurality of cooling fins and a plurality of hairpin tubes circuited through said fins, said tubes interconnected to form at least one spiral working fluid flow path having an inlet and an outlet; c) piping connecting said outlet of said at least one evaporator coil working fluid flow path to an inlet of said at least one condenser coil working fluid flow path; d) piping connecting an outlet of said at least one condenser coil working fluid flow path to an inlet of said at least one evaporator coil working fluid flow path; and e) a working fluid contained within said working fluid flow paths.
 16. The heat exchanger of claim 15, wherein said heat exchanger further comprises a plurality of fans, wherein at least one fan forces air through said evaporator coil fins and at least one fan forces air through said condenser coil fins.
 17. The heat exchanger of claim 16, wherein said working fluid is selected from the group consisting of: R-134a, R-410a, methanol, ethanol, a mixture of methanol and water, and a mixture of methanol and water. 